The initial velocity of a golf ball is what drives increases in the distance traveled by the ball, and so it is desirable to raise the initial velocity to the very limit of what is permitted under the Rules of Golf. Golf balls are made of polymeric substances, with the majority of golf balls today being solid golf balls containing a core that is obtained by molding under applied heat a rubber composition prepared by adding a crosslinking agent or organic peroxide, metal oxides and the like to a base rubber such as polybutadiene rubber. The polymeric substances making up the golf ball contain volatile substances such as the following low-molecular-weight compounds: water, various additives and their decomposition products, the decomposition products of catalysts, and residual solvents. JP-B S56-26422 teaches art which, by removing at least fixed amounts of these volatile substances, imparts a golf ball with a higher initial velocity than pre-existing golf balls and is thus able to increase the distance traveled by the ball.
That is, the foregoing art subjects all or part of a golf ball to a given heat treatment so as to remove volatile substances and, by setting the removal ratio thereof to at least 1.0%, increases the coefficient of restitution and the initial velocity. In such art, the percent removal of volatile substances is calculated from the total weight of the volatile substances that volatilize off when the prescribed treatment (heat treatment) has been carried out and the weight of the substances that is subjected to such heat treatment.
However, the foregoing art does not focus on the volatile components which remain within the golf ball. What is actually important is not how much volatile substances have volatilized, but rather, when energy is imparted to the golf ball from the head of a golf club, the degree to which that energy can be converted without loss into initial velocity. Hence, there has long existed a desire for art that reduces the loss of energy.